Final answer:
The term referring to the change in size of an individual over time is the growth rate, which can be modeled mathematically through exponential or logistic growth models, resulting in J-curve or S-curve graphs, respectively. These models take into account population size and carrying capacity to describe population dynamics in biology.
Step-by-step explanation:
The term that expresses the change in size of an individual during the observed period of time as a function of the size of the individual in a biological context is the growth rate. This concept is crucial in understanding population dynamics and is represented in mathematical models by formulas such as the exponential growth model and the logistic growth model. These models use population size, represented by 'S', and a constant, represented by 'k', to determine the growth rate over time. In particularly, the logistic growth model yields an S-shaped curve on a graph where the population growth initially increases exponentially with abundant resources, then decreases as resources become limited, and finally levels off at the carrying capacity of the environment.
Graphical representations, such as Curve A showing an exponential pattern of growth and Curve B showing a logistic pattern, help illustrate the different stages of population growth and the factors that may affect these stages, including the onset of birth rate decrease and the interaction with environmental carrying capacity.